1. Field of the Invention
The present invention relates to a light emitting device, and more particularly, to a light emitting device capable of reducing light loss due to wavelength conversion by employing nanowire phosphors.
2. Discussion of the Background
U.S. Pat. No. 6,812,500 discloses a light emitting device comprising a GaN-based, particularly, AlInGaN-based light emitting diode capable of emitting ultraviolet or blue light, and phosphors absorbing a portion of light emitted from the light emitting diode and emitting light with converted wavelengths, thereby implementing polychromatic light, e.g., white light. Since such a white light emitting device uses a single-wavelength light source as a light source, its structure is very simple as compared with a white light emitting device using a plurality of light sources for different wavelengths.
Examples of phosphors used in the white light emitting device include an YAG:Ce phosphor using Ce3+ as an activator, an orthosilicate phosphor represented by Sr2SiO4:Eu using Eu2+ as an activator, and a thiogallate phosphor such as CaGa2S4:Eu.
These phosphors are generally prepared in a powder form through a solid state reaction method, and high-purity raw materials and strict stoichiometric compositions are required to synthesize these phosphors. Particularly, heat treatment at a high temperature of 1300° C. or more is required to synthesize YAG:Ce. This raises costs of the phosphors, leading to increase in manufacturing costs of the white light emitting device.
Further, since each of these powdered phosphors has many traps therein, it is likely to cause non-radiative recombination. Such non-radiative recombination leads to light loss, resulting in considerable reduction of wavelength conversion efficiency.